Low-activation materials with isotopic tailoring for future NPPs

The purpose of paper is in studying perspectives of new structural materials and coolants for nuclear power plants (NPPs). The main concern is for their improvement using an isotopic tailoring technique to reduce post irradiation activity. Two types of materials are explored. The first one is zirconium alloy widely used in thermal reactors as a structural material. Calculation of zirconium activation for the thermal reactor spectrum was carried out and accumulation of long-lived zirconium isotope, Zr-93, has been shown. The opportunity for reducing Zr-93 generation by enriching natural zirconium with zirconium isotope, Zr-90, is analyzed. It is shown that enrichment up to 99 percent permits the tailored material to reach the clearance level of activity in 5 years after shutdown. Another material, which can be isotopically tailored, is molten lead used in fast reactors as a coolant. Calculation using the FISPACT-3 code shows that 30 years irradiation of natural lead (Pb-nat), leads to accumulation of long-lived toxic radionuclides, Bi-207, Bi-208, and Pb-210, that extends the cooling time of activity to the clearance level up to 50 years. For using lead isotope, Pb-206, instead of Pb-nat it is possible to shorten this time to one month. In this case, the concentration of the most toxic radionuclide polonium isotope, Po-210, essentially decreases. Thus, zirconium enriched by Zr-90 and lead enriched by Pb-206 can be considered as low-activation materials for the future reactor technology